Lead sulfide, roasting

Roasting. Copper and lead sulfides are direcdy smelted but not zinc sulfide. However, theoretical calculations are encouraging (20) and, if an efficient means of condensing zinc rapidly from 1600 K in the presence of carbon dioxide, sulfur dioxide, and steam can be devised, the process may be feasible. The reaction of zinc vapor to yield zinc oxide or zinc sulfide presents the main difficulty. 

When galena, a lead ore (composed of lead sulfide) is roasted in a well-ventilated, open furnace, part of the lead is oxidized by air oxygen to lead oxide and the sulfur to sulfur dioxide, which is released into the atmosphere (see Textbox 33) ... 

It also is produced when lead sulfide is roasted in air. 

Metallurgy. After concentration of sulfide ores of lead (usually by flotation), the concentrate is subjected to an incomplete process of roasting. This treatment converts lead sulfide partly to lead monoxide and lead sulfate... 

The most important ore of lead is galena, (PbS). To recover the metal, this sulfide may be first roasted to PbO, to PbS04, or to a mixture of the two. However, both the sulfate and the oxide react with excess lead sulfide at high temperatures to yield lead metal and sulfur dioxide. PbO may also be reduced using carbon or carbon monoxide. 

Derivation Roasting and reduction of galena (lead sulfide), anglesite (lead sulfate), and cerussite (lead carbonate). Also from scrap. 

Many metals occur in nature as sulfides. The process of extracting the free (elemental) metals involves roasting—heating an ore in the presence of air. For many metal sulfides this produces a metal oxide and SO2. The metal oxides are then reduced to the free metals. Consider lead sulfide, PhS, as an example. 

Metallurgy, the process of producing a metal from its ore, always involves oxidation-reduction reactions. In the metallurgy of galena (PbS), the principal lead-containing ore, the first step is the conversion of lead sulfide to its oxide (a process called roasting). 

This experiment illustrates two of the reactions that occur during the production of lead from lead sulfide ore. The ore is first roasted to convert some or all of the sufide to lead monoxide. The monoxide can be reduced to lead by either reducing it with carbon or simply by heating it in the absence of air with more lead sulfide. 

The gases produced from desulfurization of lead ores contain varying concentrations of SO2 and dust, similar to gases produced during copper and zinc sulfide roasting. 

For the standard reverberatory furnace, a batch of galena was added to the furnace hearth and was roasted with hand-rabbling for about two hours, in which time part of the lead sulfide was directly oxidised to lead sulfate. The resulting mixture of lead sulfate and unreacted lead sulfide was thoroughly mixed and the temperature of the furnace was increased. This allowed the roast reaction , as given in Equation 2.1, to take place, with copious emission of sulfur dioxide ... 

In practice, for the sintering of lead sulfide concentrates, a sulfide sulfur content of the charge of around six to seven per cent is required to achieve the necessary peak bed tanperature. Since lead concentrates normally range from 15 per cent to 25 per cent sulfide sulfur they must either be diluted or partially roasted before sintering. Some dilution with return material occurs, but dilution with recycled sinter is the preferred approach because of the high degree of control over the sinter feed mix... 

In the selective flotation of zinc-lead sulfide ores, cadmium is distributed between ZnS and PbS concentrates. When heated to high enough temperature (1100°C), as is the case during roasting of lead concentrates, CdS volatiHzes without decomposition and is found in the dust collected in bag filters or in electrostatic precipitators. Dur-... 

The tonnages involved are illustrated in Tables 8.1 and 8.2, which indicate the annual production of copper, lead, zinc, and pyrites in the world and in the United States, respectively. The actual course of the roasting operations is illustrated by the following example using lead sulfide ... 

As an example of these processes, the original creation of lead metal probably resulted from the observation of lead metal flowing out of fires when galena (lead sulfide) was used as the rocks to surround fire pits. The galena rocks were roasted to form lead oxide. This oxidation product and charcoal in the fire reacted to form lead metal while emitting sulfur dioxide, carbon dioxide,... 

Particles of low-grade lead sulfide are roasted to produce a porous lead oxide ash. At the center of the ore particles is a core of unreacted sulfide. The oxygen permeability in this core is much less than in the ash. Thus this reaction is best modeled as heterogeneous, occurring at the interface between ore and ash. 

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